Interesting Question / Challenge

I have an interesting challenge and was hoping one of the gurus can assist.

I have a program running on a client machine that I need to "trigger". The program is written in VB.NET.

What is the easiest way I can generate a "trigger" to that client machine?

Couple of things I already considered:
a) check for a presence of some file (too cumbersome)
b) implement sockets and listen on some port for a trigger (too complex, error prone)
c) check some website for a presense of something and use that as trigger (too much work, must setup site, read it ...)

... is there anything simple that anyone can think of? Ideally if I could "ping to a port" and then have the client just listen to any activity on the port would be ideal, but I don't know if this is possible.

I'm not sure and clear on what exactly you want but no offense but it sound more like you want to do something else here. What the main purpose of trigging the client? Is the program that will trigger the client will be installed on a clients computer or remotely?

THe program that I want to "trigger" will be installed on the client computer. Once it sees the trigger it will then need to do something, and then go back to "sleep". Basically, my question is how can I "trigger it" easily.

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